The present invention relates to a rewinding method for making logs starting from a web, for example used for the production of rolls of toilet paper, rolls of all purpose wipers, household non woven fabric, industrial rolls and the like.
Furthermore, the invention relates to a rewinding machine that carries out this method.
Rewinding machines are known wherein a winding step is carried out on a log which is in contact surface with winding rollers. More precisely, the log is formed starting from a web of paper, continuous or with transversal perforations, which is carried by first dragging means, is wound partially on an upper winding roller, is in contact with a lower winding roller and is kept against the two upper and lower winding rollers by means of a pressure roller. The three rollers define a channel, or winding cradle, wherein the log is formed and the web of paper is supplied continuously and pulled by the surface frictional contact of the rollers on the log.
Normally, in the winding cradle the log is formed on a tubular core. Once the log has reached a predetermined diameter, normally calculated by checking the length of the developed paper, the web is cut or torn and the log is pushed away from the winding cradle at the side of the lower winding roller and, at the same time, a new core is supplied into the cradle by a pusher. It is possible, however, to wind the log without core as well.
Some types of rewinding machines, at the end of each roll winding step, provide a blade that cuts transversally the web by pressing against the upper winding roller. The upper winding roller has one or more cutting slits with which a retractable blade engages mounted on an adjacent cutting roller. This system has the drawback that it does not allow cuts having length not multiple of the circumference of the upper winding roller, or not multiple of the distance between two successive cutting slits when several cutting slits are provided for.
In the case, instead, of rewinding machines in which the web is torn, there is the drawback that the tearing step is subject to being carried out incorrectly. Actually, the web is stopped upstream of, or onto, the upper winding roller and the tearing is caused by the pulling action, on the web kept still, of the lower winding roller, on which the log is pushed by the pressure roller. Normally, it is sufficient to create a speed difference between said two rollers at the moment of the exchange in order to effect the tearing. However, the tearing sometimes cannot be made correctly, since it depends on the correct growth of the log being wound as well as on the presence and quality of the transversal perforation. Furthermore, with the tearing method rolls can be obtained whose development is multiple of the pitch between two transversal perforations only. Finally, in case of rolls without transversal perforations, for example industrial rolls, in order to effect the tearing it is necessary to make a special auxiliary perforation on the web at the end of the development of each roll.
It is an object of the present invention to provide a rewinding method of a web of paper for making logs, wherein the passage from a roll to the successive one is carried out by cutting the web and wherein the development of the web wound on the log after the cutting step has whichever desired length.
It is another object of the present invention to provide a rewinding machine of a web of paper for making logs that is capable of cutting the web upstream the winding zone in a desired location.
These and other objects are achieved by the web winding method for making a log whose characteristic is that it comprises the steps of:
feeding a web of paper in a winding cradle;
arranging upstream of the cradle a counter support roller that comprises at least a cutting slit transversal to the web;
arranging a cutting roller that faces the counter support roller and comprises at least a blade transversal to the web, the web running between the counter support roller and the cutting roller;
cutting or locally tearing the web for contact of the blade with the web in a predetermined moment at the slit of the counter support roller, the cut creating in the web a tail end and a front end;
concluding the winding of the log that comprises the tail end and introducing the front end in the cradle for starting the winding of a new log;
winding the new log up to a predetermined development of the web;
decelerating or accelerating the counter support roller making it slide on the web while winding the new log so that the blade is ready to cut the web at a desired chosen location.
Preferably, the front end is pulled towards the winding cradle by a suction step carried out by the counter support roller.
Always preferably, the winding cradle comprises an upper winding roller, a lower winding roller and a pressure roller, the upper winding roller comprising suction means for capturing at least the front end of the web and starting the winding of the new log.
In a preferred embodiment, the upper winding roller has a plurality of radial holes, the front end of the web being captured by a predetermined sector of said holes belonging to an outer drum by means of an inner drum rotatable coaxially but in a way independent from the outer drum and suitable for selectively connecting the predetermined sector of the holes with a suction chamber.
The synchronization between the inner drum, the cutting roller and the counter support roller is obtained by a control step of driven axes operated by a computer, whereby, for every chosen web development between two successive cuts the computer arranges a reset phase of the counter support roller with respect to the blade and a relative rotation between the outer drum and the inner drum.
According to another aspect of the present invention, a rewinding apparatus of a web for making logs comprises:
means for feeding and dragging a web of paper;
a winding cradle wherein the winding of the log is carried out downstream the means for feeding;
a counter support roller on which the web lays located in the space interval between the means for feeding and the cradle, the counter support roller having at least a cutting slit;
a cutting roller suitable for bringing periodically a cutting blade against the counter support roller at its slit for cutting the web;
means for accelerating or decelerating the counter support roller and the cutting roller with respect to the web.
The cutting blade urges against the counter support roller for cutting the web creating a tail end of the previous log and a front end of a new log. Preferably, the counter support roller comprises suction means for dragging the front end towards the winding cradle.
Always preferably, the winding cradle comprises an upper winding roller, a lower winding roller and a pressure roller, the upper winding roller comprising means for capturing the front end of the web, said means for capturing may be suction means.
The upper winding roller comprises preferably an outer drum having a plurality of holes and an inner drum rotatable independently from the outer drum and suitable for connecting a predetermined sector of the holes with a suction chamber, whereby it is possible in turn to capture the front end by means of a predetermined sector of the outer drum.
In an advantageous embodiment of the invention the inner drum, the counter support roller and the cutting roller are brought into rotation by axes driven by at least a motor operated by a control unit that adjusts the cutting length of the web of said log, the motor decelerating or accelerating the rotation of said axes and causing said counter support roller to slide with respect to said web.
In order to make the sliding lighter the counter support roller has a surface with a plurality of small air blowing holes for reducing further the friction with respect to said web during the sliding step.